4x^3-x
=x(4x²-1)
=x(2x-1)(2x+1)
（x+y）^2-9x^2
=(x+y-3x)(x+y+3x)
=(y-2x)(y+4x)
x^2-y^2+2（x-y）
=(x-y)(x+y)+2(x-y)
=(x-y)(x+y+2)
8（x^2-2y^2）-x（7x+y）+xy、
=8x²-16y²-7x²-xy+xy
=x²-16y²
=(x-4y)(x+4y)